Cryptosporidium parvum is a major cause of diarrheal disease among immunocompromised AIDS patients with limited treatment options. The overall goal of the present proposal is to develop therapeutic plantibodies for AIDS-associated diarrheal diseases. This approach will provide a novel and inexpensive means to prevent and/or treat Cryptosporidium parvum diarrhea. Previous work demonstrates that anti- Cryptosporidium antibodies given as colostrum effectively reduced diarrhea and shedding of oocysts in AIDS patients. Plantibodies offer an inexpensive alternative to colostrum. Degenerate PCR primers will be used to clone and sequence the heavy and light chain variable region genes from a neutralizing murine monoclonal antibody to Cryptosporidium parvum. This antibody administered by mouth previously was shown to block infection in mice infected with Cryptosporidium parvum oocysts. The antibody genes will be expressed as in an IgA expression vector and tested in alfalfa protoplasts prior to transfer to transgenic plants. This approach will provide a novel and inexpensive means to make and deliver antibodies to prevent or treat this important human pathogen. PROPOSED COMMERCIAL APPLICATION: Construction of plantibody anti- Cryptosporidium parvum MAB will provide a novel therapeutic for treatment of this severe diarrheal disease.